1,042 research outputs found
Proposed method for searches of gravitational waves from PKS 2155-304 and other blazar flares
We propose to search for gravitational waves from PKS 2155-304 as well as
other blazars. PKS 2155-304 emitted a long duration energetic flare in July
2006, with total isotropic equivalent energy released in TeV gamma rays of
approximately ergs. Any possible gravitational wave signals
associated with this outburst should be seen by gravitational wave detectors at
the same time as the electromagnetic signal. During this flare, the two LIGO
interferometers at Hanford and the GEO detector were in operation and
collecting data. For this search we will use the data from multiple
gravitational wave detectors. The method we use for this purpose is a coherent
network analysis algorithm and is called {\tt RIDGE}. To estimate the
sensitivity of the search, we perform numerical simulations. The sensitivity to
estimated gravitational wave energy at the source is about
ergs for a detection probability of 20%. For this search, an end-to-end
analysis pipeline has been developed, which takes into account the motion of
the source across the sky.Comment: 10 pages, 7 figures. Contribution to 12th Gravitational Wave Data
Analysis Workshop. Submitted to Classical and Quantum Gravity. Changes in
response to referee comment
Model-independent test of gravity with a network of ground-based gravitational-wave detectors
The observation of gravitational waves with a global network of
interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will
make it possible to probe into the nature of space-time structure. Besides
Einstein's general theory of relativity, there are several theories of
gravitation that passed experimental tests so far. The gravitational-wave
observation provides a new experimental test of alternative theories of gravity
because a gravitational wave may have at most six independent modes of
polarization, of which properties and number of modes are dependent on theories
of gravity. This paper proposes a method to reconstruct the independent modes
of polarization in time-series data of an advanced detector network. Since the
method does not rely on any specific model, it gives model-independent test of
alternative theories of gravity
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Latent tuberculosis infection screening of adult close contacts in London: a cost-utility analysis
Background: The National Institute for Health and Care Excellence (NICE) guidelines in 2016 recommend tuberculin skin test (TST) at a 5 mm induration size cut-off for latent tuberculosis infection (LTBI) screening of adult close contacts of active tuberculosis (TB) cases. An alternative would be to use an interferon-gamma release assay (IGRA) which has a higher specificity, such as the QuantiFERON-TB Gold in Tube (QFT-GIT) or T-SPOT.TB (T-SPOT). We aimed to evaluate the cost-effectiveness of the screening and treatment of LTBI in adult close contacts with various combinations of these tests in a representative London cohort.
Methods: Clinical data of adult close contacts of pulmonary TB cases who were recommended to receive TST and IGRA in a TB clinic in London between 2008 and 2010 were retrospectively reviewed. A Markov decision analytic model, using an NHS perspective and lifetime horizon, was used to compare costs and quality-adjusted life-years (QALYs) associated with 7 screening strategies followed by chemoprophylaxis: TST alone, IGRA (QFT-GIT or T-SPOT) alone, TST positive followed by IGRA, and TST negative followed by IGRA. Future costs and QALYs were discounted at 3.5% per year.
Results: 381 asymptomatic close contacts aged 18 to 65 years were included in this study. The mean age was 35.2 years and the majority (75.3%) were BCG vaccinated. In the base-case analysis, QFT-GIT was the most cost-effective strategy with £6876 per QALY gained, compared to TST positive followed by QFT-GIT strategy. QFT-GIT alone averted 1.6 TB cases per 1000 contacts compared to TST positive followed by QFT-GIT.
Conclusion: Of the considered testing strategies, the QFT-GIT alone is preferable for LTBI screening in adult close contacts of pulmonary TB cases in London
Searching for nontensorial polarizations of stochastic gravitational waves with laser interferometers
Searches for gravitational waves associated with pulsar glitches using a coherent network algorithm
Pulsar glitches are a potential source of gravitational waves for current and
future interferometric gravitational wave detectors. Some pulsar glitch events
were observed by radio and X-ray telescopes during the fifth LIGO science run.
It is expected that glitches from these same pulsars should also be seen in the
future. We carried out Monte Carlo simulations to estimate the sensitivity of
possible gravitational wave signals associated with a pulsar glitch using a
coherent network analysis method. We show the detection efficiency and evaluate
the reconstruction accuracy of gravitational waveforms using a matched filter
analysis on the estimated gravitational waveforms from the coherent analysis
algorithm.Comment: submitted to CQ
The hydration structure of Cu2+: More tetrahedral than octahedral?
A comprehensive multi-technique approach has been used to address the controversial question of the preferred geometric form of the Cu2+ aqua-ion hydration shell. A combination of H/D isotopic substitution neutron scattering and X-ray scattering has been used to refine atomistic models of 0.5 m and 2.0 m solutions of Cu(ClO4)2, that have also been constrained to simultaneously reproduce detailed local structure information about the cation environment obtained by X-ray Absorption spectroscopy. The adoption of the Empirical Potential Structure Refinement (EPSR) technique as a single unified analytical framework minimises the chances for biasing the result in favour of a specific pre-conceived outcome. The results are consistent with an average coordination for each Cu2+ ion of 4.5 ± 0.6 water molecules that matches the more recent picture of five-fold coordination in a 2.0 m solution, but interestingly this combined study highlights that the preferred local geometry of the ion sites is found to have a mixed character of tetrahedral, trigonal bipyramidal and octahedral components. A further point to note is that this new model adds support to a largely ignored result in the literature relating to the linear electric field effect induced g-shifts observed in the electron paramagnetic resonance spectra of glassy Cu2+ complexes (Peisach and Mims, Chem. Phys. Lett., 1976, 37, 307–310) that first highlighted the importance of tetrahedral distortions in the cation's hydration shell structure
Probing non-tensorial polarizations of stochastic gravitational-wave backgrounds with ground-based laser interferometers
In a general metric theory of gravitation in four dimensions, six
polarizations of a gravitational wave are allowed: two scalar and two vector
modes, in addition to two tensor modes in general relativity. Such additional
polarization modes appear due to additional degrees of freedom in modified
theories of gravitation or theories with extra dimensions. Thus, observations
of gravitational waves can be utilized to constrain the extended models of
gravitation. In this paper, we investigate detectability of additional
polarization modes of gravitational waves, particularly focusing on a
stochastic gravitational-wave background, with laser-interferometric detectors
on the Earth. We found that multiple detectors can separate the mixture of
polarization modes in detector outputs, and that they have almost the same
sensitivity to each polarization mode of stochastic gravitational-wave
background.Comment: 18 pages, 13 figure
A multiple-beam CLEAN for imaging intra-day variable radio sources
The CLEAN algorithm, widely used in radio interferometry for the
deconvolution of radio images, performs well only if the raw radio image (dirty
image) is, to good approximation, a simple convolution between the instrumental
point-spread function (dirty beam) and the true distribution of emission across
the sky. An important case in which this approximation breaks down is during
frequency synthesis if the observing bandwidth is wide enough for variations in
the spectrum of the sky to become significant. The convolution assumption also
breaks down, in any situation but snapshot observations, if sources in the
field vary significantly in flux density over the duration of the observation.
Such time-variation can even be instrumental in nature, for example due to
jitter or rotation of the primary beam pattern on the sky during an
observation. An algorithm already exists for dealing with the spectral
variation encountered in wide-band frequency synthesis interferometry. This
algorithm is an extension of CLEAN in which, at each iteration, a set of N
`dirty beams' are fitted and subtracted in parallel, instead of just a single
dirty beam as in standard CLEAN. In the wide-band algorithm the beams are
obtained by expanding a nominal source spectrum in a Taylor series, each term
of the series generating one of the beams. In the present paper this algorithm
is extended to images which contain sources which vary over both frequency and
time. Different expansion schemes (or bases) on the time and frequency axes are
compared, and issues such as Gibbs ringing and non-orthogonality are discussed.
It is shown that practical considerations make it often desirable to
orthogonalize the set of beams before commencing the cleaning. This is easily
accomplished via a Gram-Schmidt technique.Comment: 9 pages, 7 figures. Accepted for publication in A&
Prospects for improving the sensitivity of KAGRA gravitational wave detector
KAGRA is a new gravitational wave detector which aims to begin joint observation with Advanced LIGO and Advanced Virgo from late 2019. Here, we present KAGRA's possible upgrade plans to improve the sensitivity in the decade ahead. Unlike other state-of-the-art detectors, KAGRA requires different investigations for the upgrade since it is the only detector which employs cryogenic cooling of the test mass mirrors. In this paper, investigations on the upgrade plans which can be realized by changing the input laser power, increasing the mirror mass, and injecting frequency dependent squeezed vacuum are presented. We show how each upgrade affects to the detector frequency bands and also discuss impacts on gravitational-wave science. We then propose an effective progression of upgrades based on technical feasibility and scientific scenarios
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